The bony-eared assfish (''Acanthonus armatus'') is a

bathypelagic The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above and the abyssopelagic below. The bathypela ...

species of

cusk-eel The cusk-eel family, Ophidiidae, is a group of marine bony fishes in the Ophidiiformes order. The scientific name is from the Greek ''ophis'' meaning "snake", and refers to their eel-like appearance. True eels diverged from other ray-finned fi ...

found in

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

and

sub-tropical The subtropical zones or subtropics are geographical and climate zones immediately to the north and south of the tropics. Geographically part of the temperate zones of both hemispheres, they cover the middle latitudes from to approximately 3 ...

oceans at depths of from . It has been found as far north as Queen Charlotte Sound off

British Columbia British Columbia is the westernmost Provinces and territories of Canada, province of Canada. Situated in the Pacific Northwest between the Pacific Ocean and the Rocky Mountains, the province has a diverse geography, with rugged landscapes that ...

's coast. This species grows to a length of

standard length Fish measurement is the measuring of individual fish and various parts of fish anatomy, their anatomies, for data used in many areas of ichthyology, including Taxonomy (biology), taxonomy and fishery biology. Overall length Standard length (SL) is ...

. The larvae are similar in overall form to the related gargoyle cusk, but have elongated 3rd, 4th, and 5th pectoral-fin rays. The bony-eared assfish is by some sources believed to have the smallest brain-to-body weight ratio of any vertebrate. Like many other creatures that dwell in the depths of the sea, assfish are soft and flabby with a light skeleton. This is likely to have resulted from a lack of food and the high pressures which accompany living at such a depth, making it difficult to generate muscle and bone.

Etymology

The type specimen was an individual taken by the ''Challenger'' expedition (1872–1876) north of New Guinea at a depth of . It was described in 1878 by German

ichthyologist Ichthyology is the branch of zoology devoted to the study of fish, including bony fish (Osteichthyes), cartilaginous fish (Chondrichthyes), and jawless fish (Agnatha). According to FishBase, 35,800 species of fish had been described as of March 2 ...

Albert Günther Albert Karl Ludwig Gotthilf Günther , also Albert Charles Lewis Gotthilf Günther (3October 18301February 1914), was a German-born British zoologist, ichthyologist, and herpetologist. Günther is ranked the second-most productive reptile tax ...

, who gave the species its scientific name. means "armed" in Latin, likely chosen because the fish sports spines off the tip of the nose and the gills. This also perhaps accounts for the "bony-eared" part, according to Gavin Hanke, curator of vertebrate zoology at the

Royal British Columbia Museum The Royal British Columbia Museum (or Royal BC Museum), founded in 1886, is a history museum in Victoria, British Columbia, Canada. The "Royal" title was approved by Queen Elizabeth II and bestowed by Prince Philip in 1987, to coincide with a ...

. is Ancient Greek for "prickly", and ''onus'' could either mean "hake, a relative of cod", Hanke says, "or a donkey". Adam Summers, associate director at the Friday Harbor Laboratories at the University of Washington, concurs, saying ''onus'' could easily read "as a homonym of the Greek word for ass".

References

Ophidiidae Fish described in 1878 Deep sea fish Taxa named by Albert Günther {{Ophidiidae-stub